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Mar 15, 2009 | 10:55 AM

bozzzz94

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Idle:up-down

Good Morning Folks-
Started having this problem 2 weeks ago. Just haven't gotten to looking yet. When I start my van it will idle at 800 rpm then up to 1000. Stays at 800 (count 1,001-1,002-1,300-1,400) then it idles up to a grand then starts over again. Van runs fine while driving-just really noticeable at idle or pulling up to a light then sitting there. Slip it out of gear and not as noticeable, but still there. 1994 4.0 ltr. 193 grand on the O.D. I haven't tried pulling any codes yet. What do you think?-Thanks Boz

Mar 15, 2009 | 05:26 PM

Pablo-UA

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From: Kiev, Ukraine

well, usually this is IAC issue. Just unscre 6 mm bolts this valve is held with and take appart (remove small solenoid held with philips head 4mm bolts). Use TB cleaner to clean.

Well IAC valve is PWM controlled with small transistor swith. And sometimes it gets stuck. I have similar problem. My IAC have some 2-4 sec delay when it is cold outdoors. I release gas pedal and wait for 2-4 sec. to let engine decrease idle speed. when engine is hot, everething is Ok

Mar 15, 2009 | 10:28 PM

96_4wdr

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From: Washington state

also check the throttle body plate to body gap. they become gummed up and sticky over time with PCV injested gases, dirt/dust air filter leak thru.
causes intermittent idle problems and changes idle mix thus the IAC is ordered to compensate by the PCM. where it stops is anyones guess

i clean the throttle body every 30k miles or so with spray cleaner and wipe out with old T shirt. Ford says don't touch the non stick coating they put on the interior of the TB but their Teflon doesnt' work.

can also be the TPS, worn intermittent spot at bottom end

Mar 16, 2009 | 03:49 AM

Pablo-UA

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From: Kiev, Ukraine

TPS is really easy to check measurig voltage on center terminal. for idle - 0.4-0.8V

Mar 16, 2009 | 03:32 PM

xlt4wd90

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From: SoCal

Quote:

Originally Posted by Pablo-UA

My IAC have some 2-4 sec delay when it is cold outdoors. I release gas pedal and wait for 2-4 sec. to let engine decrease idle speed. when engine is hot, everething is Ok

The IAC also serves as the anti-decel valve that used to be on carburetors. It slows down the closing of the throttle so that the fuel that has accumulated on the walls of the intake manifold and ports do not vaporize all at once, creating an excessively rich condition. I'm guessing when the engine is cold, this delay is lengthened, as the EEC will try to use richer mixtures when cold, which causes even more wall-wetting.

The opposite occurs when the throttle is opened; an increase in pressure causes vaporized fuel to condense on the colder walls of the intake tract, causing a lean condition. This is compensated for by acceleration enrichment by the carburetor pump or extra pulses in the fuel injector.

Mar 16, 2009 | 04:26 PM

Pablo-UA

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From: Kiev, Ukraine

this hypotesa is easy to test. I can cinnect LED to IAC and see is it controlled ore not

Mar 16, 2009 | 04:37 PM

Aeroman59

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From: Kitchener,Ontario,Canada

IAC seems to be attempting to control idle speed. At this point 96's explanation makes a lot of sense. Look for gum in the throtte valve. IAC problem would tend to give a more random/erratic idle speed.
Aeroman.

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Mar 17, 2009 | 02:34 PM

Pablo-UA

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From: Kiev, Ukraine

well, seems wierd... I connected LED to IAC and what I see? when IAC is disangaged RPM drops in 1-2 seconds, not immideatly

Mar 21, 2009 | 10:58 AM

#10

bozzzz94

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Thank Q for all of the leads. i just got back from a military TDY. I'll start off with what Pablo said and work my way down the list then let ya know what I find. Thanks again folks.

Mar 21, 2009 | 12:54 PM

#11

Aeroman59

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From: Kitchener,Ontario,Canada

Quote:

Originally Posted by 96_4wdr

i clean the throttle body every 30k miles or so with spray cleaner and wipe out with old T shirt. Ford says don't touch the non stick coating they put on the interior of the TB but their Teflon doesnt' work.

can also be the TPS, worn intermittent spot at bottom end

Teflon does work, problem is only works for a few years & then it's worse than nothing at all. Just like that old frying pan in the cupboard which the eggs stick to.